1. Field of the Invention
The present invention relates to an ink-jet printhead. More particularly, the present invention relates to a monolithic ink-jet printhead having a hemispheric ink chamber and working in a bubble-jet mode, and a method for manufacturing the same.
2. Description of the Related Art
In general, ink-jet printheads eject small ink droplets for printing at a desired position on a paper and print out images having predetermined colors. Ink ejection methods for ink-jet printers include an electro-thermal transducer method (bubble-jet type) for ejecting an ink droplet by generating bubbles in ink using a heat source, and an electromechanical transducer method for ejecting an ink droplet according to a variation in the volume of ink caused by the deformation of a piezoelectric body.
In a bubble-jet type ink ejection mechanism, as mentioned above, when power is applied to a heater comprised of a resistance heating element, ink adjacent to the heater is rapidly heated to about 300xc2x0 C. Heating the ink generates bubbles, which grow and swell, and thus apply pressure in the ink chamber filled with the ink. As a result, ink adjacent to a nozzle is ejected from the ink chamber through the nozzle.
There are multiple factors and parameters to consider in making an ink-jet printhead having an ink ejecting unit in a bubble-jet mode. First, it should be simple to manufacture, have a low manufacturing cost, and be capable of being mass-produced. Second, in order to produce high quality color images, the formation of undesirable satellite ink droplets that usually accompany an ejected main ink droplet must be avoided during the printing process. Third, cross-talk between adjacent nozzles, from which ink is not ejected, must be avoided, when ink is ejected from one nozzle, or when an ink chamber is refilled with ink after ink is ejected. For this purpose, ink back flow, i.e., when ink flows in a direction opposite to the direction in which ink is ejected, should be prevented. Fourth, for high-speed printing, the refilling period after ink is ejected should be as short a period of time as possible to increase the printing speed. That is, the driving frequency of the printhead should be high.
The above requirements, however, tend to conflict with one another. Furthermore, the performance of an ink-jet printhead is closely related to and affected by the structure and design, e.g., the relative sizes of ink chamber, ink passage, and heater, etc., as well as by the formation and expansion shape of the bubbles.
FIGS. 1A and 1B illustrate a conventional bubble-jet type ink-jet printhead according to the prior art. FIG. 1A is an exploded perspective view illustrating the structure of a conventional ink ejecting unit. FIG. 1B illustrates a cross-sectional view of the ejection of an ink droplet from the conventional bubble-jet type ink-jet printhead illustrated in FIG. 1A.
The conventional bubble-jet type ink-jet printhead shown in FIGS. 1A and 1B includes a substrate 10, a barrier wall 12 formed on the substrate 10 for forming an ink chamber 13 to be filled with ink 19, a heater 14 installed in the ink chamber 13, and a nozzle plate 11 in which nozzles 16, from which an ink droplet 19xe2x80x2 is ejected, are formed. The ink chamber 13 is filled with ink 19 through an ink channel 15. The nozzle 16, which is in flow communication with the ink chamber 13, is filled with ink 19 due to a capillary action. In the above structure, if current is supplied to the heater 14, the heater 14 generates heat. The heat forms a bubble 18 in the ink 19 in the ink chamber 13. The bubble 18 swells applies pressure to the ink 19 in the ink chamber 13, and the ink droplet 19xe2x80x2 is pushed out through the nozzle 16. Next, the ink 19 is absorbed through the ink channel 15, and the ink chamber 13 is refilled with the ink 19.
In the conventional printhead, however, the ink channel 15 is connected to a side of the ink chamber 13, and a width of the ink channel 15 is large. Therefore, back flow of the ink 19 easily occurs when swelling of the bubble 18 appears. In order to manufacture a printhead having the above structure, the nozzle plate 11 and the substrate 10 should be separately manufactured and bonded to each other, resulting in a complicated manufacturing process and often causing misalignment when the nozzle plate 11 is bonded to the substrate 10.
FIG. 2 illustrates a cross-sectional view of the structure of another conventional ink ejecting unit according to the prior art.
In the conventional ink-jet printhead shown in FIG. 2, ink 29 passes over the edges of a substrate 22 through an ink channel 25 formed in a print cartridge body 20 from an ink reservoir and flows into an ink chamber 23. When the heater 24 generates heat, bubbles 28 formed in the ink chamber 23 swell, and thus the ink 29 is ejected through nozzles 26 in a droplet form.
Even in the printhead having the above structure, however, a polymer tape 21, in which the nozzles 26 are formed, should be bonded to a top end of the print cartridge body 20 using an adhesive seal 31, and the substrate 22, on which the heater 24 is mounted, is installed in the print cartridge body 20. Then the substrate should be bonded to the polymer tape 21 by placing a thin adhesive layer 32 between the polymer tape 21 and the substrate 22. As with the first conventional printhead manufacturing process, the above printhead manufacturing process is complicated, and misalignment may occur in the bonding process of the elements.
In an effort to solve the above problems, it is a feature of an embodiment of the present invention to provide a bubble-jet type ink-jet printhead having a hemispheric ink chamber, in which the elements of the ink-jet printhead and a MOS integrated circuit are formed monolithically on a substrate, and a method for manufacturing the same.
Accordingly, to provide the above feature, according to one aspect of the present invention, there is provided a monolithic ink-jet printhead including a substrate on which a manifold for supplying ink, an ink chamber filled with ink to be ejected, the ink chamber having a hemispheric shape, and an ink channel for supplying ink to the ink chamber from the manifold are formed monolithically, a silicon oxide layer, in which a nozzle for ejecting ink is formed in a position corresponding to a center of the ink chamber, the silicon oxide layer being deposited on the substrate, a heater formed on the silicon oxide layer to surround the nozzle, and a MOS integrated circuit mounted on the substrate to drive the heater, the MOS integrated circuit including a MOSFET and electrodes connected to the heater. The silicon oxide layer, the heater, and the MOS integrated circuit are formed monolithically on the substrate.
It is preferable that a coating layer formed of diamond-like carbon (DLC) is formed on an external surface of the printhead. The DLC coating layer has high hydrophobic property and durability.
Preferably, the MOSFET includes a gate, formed on a gate oxide layer using the silicon oxide layer as the gate oxide layer, and source and drain regions, formed under the silicon oxide layer. It is also preferable that the heater and the gate of the MOSFET are formed of the same material. It is also preferable that a field oxide layer thicker than the silicon oxide layer is formed as an insulating layer around the MOSFET.
Further, it is also preferable that a first passivation layer is formed on the heater and on the MOSFET, and a second passivation layer is formed on the electrodes. Also preferably, the first passivation layer includes a silicon nitride layer and the second passivation layer includes tetraethylorthosilicate (TEOS) oxide layer.
Preferably, a nozzle guide extended in a direction of the depth of the ink chamber from the edges of the nozzle is formed on an upper portion of the ink chamber.
The manifold is preferably formed on the bottom surface of the substrate, and the ink channel is formed to be in flow communication with the manifold on the bottom of the ink chamber.
In a printhead according to the present invention, all of the above manufacturing and alignment requirements may be satisfied. Additionally, the elements of the printhead and a MOS integrated circuit are formed monolithically on the substrate, thereby achieving a more compact printhead.
In addition, to provide the above feature, according to another aspect of the present invention, there is provided a method for manufacturing a monolithic ink-jet printhead. The method includes preparing a silicon substrate, forming a first silicon oxide layer by oxidizing the surface of the substrate, forming on the substrate a MOS integrated circuit including a MOSFET for driving the heater and electrodes connected to the heater, forming a heater on a second silicon oxide layer, forming inside the heater a nozzle for ejecting ink by etching the second silicon oxide layer to a diameter smaller than that of the heater, forming a manifold for supplying ink by etching a bottom surface of the substrate, forming an ink chamber having a diameter larger than that of the heater and having a hemispheric shape by etching the substrate exposed by the nozzle, and forming an ink channel for connecting the ink chamber to the manifold by etching the bottom of the ink chamber through the nozzle.
Here, it is preferable that after forming the ink channel, the method further includes coating a coating layer formed of diamond-like carbon (DLC) on an external surface of the printhead.
Preferably, forming the MOS integrated circuit includes depositing a silicon nitride layer on the first silicon oxide layer, etching a portion of the first silicon oxide layer and the silicon nitride layer, forming a field oxide layer thicker than the first silicon oxide layer around a region in which the MOSFET is to be formed, removing the first silicon oxide layer and the silicon nitride layer, forming a second silicon oxide layer on the substrate, forming a gate of the MOSFET on a gate oxide layer using the second silicon oxide layer as the gate oxide layer, forming source and drain regions of the MOSFET under the second silicon oxide layer, and forming electrodes for electrically connecting the heater to the MOSFET.
Preferably, the gate and the heater are simultaneously formed of the same material, or the gate is formed of impurity-doped polysilicon, and the heater is formed of an alloy of tantalum and aluminum.
Preferably, a first passivation layer is formed on the heater and on the MOSFET, and the electrodes are formed on the first passivation layer, and a second passivation layer is formed on the electrodes. A boro-phosphorous-silicate glass (BPSG) layer may be coated on the first passivation layer to planarize the surface of the printhead.
Forming an ink chamber may be preformed by isotropically etching the substrate exposed by the nozzle, or by isotropically etching the substrate after anisotropically etching the substrate exposed by the nozzle, to a predetermined depth. Forming the ink chamber may also include forming a hole having a predetermined depth by anisotropically etching the substrate exposed by the nozzle, depositing a predetermined material layer to a predetermined thickness on the entire surface of the anisotropically-etched substrate, exposing a bottom of the hole by anisotropically etching the material layer and simultaneously forming a nozzle guide, which is formed of the material layer, on the sidewall of the hole, and forming the ink chamber by isotropically etching the substrate exposed to the bottom of the hole.
In the method for manufacturing a monolithic ink-jet printhead according to the present invention, the elements of an ink-jet printhead and a MOS integrated circuit may be formed monolithically on a substrate, thereby facilitating mass-production of the printhead.